Abstract: A computational model was constructed to study the separation of hydrogen isotopes by cryogenic distillation with sidestream feedback and a computational analysis was made for H₂/HD/D₂ system. The results show a remarkable influence of sidestream feedback on separation performance. D₂ is dominant in reboiler and deuterium abundance may reach 0.90 with sidestream feedback while HD is dominant in reboiler and deuterium abundance can not exceed 0.50 without sidestream feedback. A peak of transformation of HD to D₂ appears after about 40 h with sidestream while enrichment of HD is saturated without sidestream at the same time. The efficiency of deuterium stripping is best when a sidestream ratio is 1.